Explosion-proof heater



March 25, 1952 LR; MAST EXPLOSION-PROOF HEATER 3 Sheets-Sheet l FiledJan. 28, 1949 FIG. l.

@c @if INVEN-ron LOWELL f?. M1457' ATTORNEYS Filed Jan, 28. 1949 3Sheets-Sheet 2 FIG. 4.

INVENTOR LOWELL R. MAST ATTORNEYS March 25, 1952 L, R, MASTEXPLOSION-PROOF HEATER 3 Sheets-Sheet 3 Filed Jan. 28, 1949 INVENTORLOWE/.L R. MAST FIG. 6.

ATTORNEYS Patented Mar. 25, 1952 2,590,336 EXPLOSION-PROOF HEATER LowellR. Mast, East Rochester, N.

to Electromode Corporation,

Y., assigner Rochester, N. Y.-

Application January 28, 1949, Serial No. 73,369

Claims. 1

This invention relates to an proof heater. .1 One of the objects of thisinvention is to provide an electric, explosion-proof heater which issimple, practical and thoroughly durable. Another object is to provide aheater of the above character which is eicient in operation. Anotherobject is to provide a heater of the above character which can beinexpensively manufactured. Another object of this invention is toprovide a heater of the above character which can be operated safely inexplosive areas, such as atmospheres containing gasoline, petroleum,naphtha, acetone, benzol, lacquer, solvent vapors and natural gas.Another object is to provide a heater of the above character, none ofthe exposed parts of which ever become excessively hot even whenoperating under a full load. A

electric, explosion:

further object is to provide a construction of the above character inwhich the material is so disposed as to attain a high degree of strengthwithout heavy construction. Still another object is to provide a heaterof the above character which is not affected by extreme temperaturechanges. Other objects Will be in part obvious and in part pointed outhereinafter.

The invention accordingly consists in the features of construction,combinations of elements, and arrangements of parts, all as will beillustratively described herein and the scope of the application whichwill be indicated in the following claims.

In the accompanying drawings, in which is shown one of the variouspossible embodiments of this invention,

Figure l is a perspective view of a pair of heaters connected in series;

Figure 2 is an exploded perspective view of the heater;

Figure 3 is a vertical section on an enlarged scale taken on the line3-3 of Figure 1;

Figure 4 is a vertical section taken on the line 4-4 of Figure 3;

Figure 5 is a horizontal section taken on the line 5-5 of Figure 4; and

Figure 6 is a view on an enlarged scale of one of the heating elementspartly in section.

Similar reference characters refer to similar parts throughout theseveral views of the drawings.

Referring now to the drawings, in general, the heater includes anexplosion-proof connection box, generally indicated at 24 (Figure 2), onwhich are mounted a series of grid members, generally indicatedv at l8a,I8b, I8c and I 8d.

Each grid member has a heating element, generally indicated at ID inFigures 4 and 6, cast therein, the terminals 'I and I5 (Figures 3 and 4)on the lowerv ends of each heating element I0 extending into connectionbox 24. Each grid member is provided with ns which form verticalpassageways, so that when the grid member I8 and the-connection box 24are mounted in a housing, generally indicated at 9 (Figure 1), the airenters opening 9a, ilows upwardly through the grid member passagewaysand passes out of the heater through opening 9b. A baille, generallyindicated at 3I (Figures 2 and 3), is positioned rearwardly of the gridmembers and spaced from the rear plate 30 of the housing to provide apassageway for secondary air circulation between the baiile and rearplate. Each heater may be used individually or as one unit in a seriesof heaters, such as shown in Figure 1.

As all of the grid members are substantially similar in construction,specic description of the grid members will be limited to grid memberI8a. Grid member [8a is cast from aluminum or other metal-having a highthermal conductivity and includes a backbone portion` 2U (Figures 2, 4and 5) having a plurality of ns I9a and ISb formed thereon and a heatingelement I0 cast therein. As is best shown in Figure 6, heating elementI0 is U-shaped and includes a resistance wire II, the ends of which areconnected to conductors 8 and I2. The resistance II and conductors 8 andI2 are tioned within a tubular steel or copper sheath I3. The spaceintermediate resistance II and conductors 8 and I2 and the sheath I3 isiilled by an oxide powder I4 which-is a highly elcient electricalinsulator and at the same time a good conductor of heat. Conductors 8and I2 are connected to terminals I and I5,Which.in turn are connectedto wires leading to an external pOwer source (not shown).

Terminals I and I5 have collar portions 4I and IB (Figure 6) whichsupport insulators 42 and I1 mounted onvthe-lower ends of conductors 8and I2. Insulators I'l and 42 insulate conductors 8 and I2 from sheathI3, insulate sheath I3 from terminals 1 and I5, and also serve to holdthe oxide powder I4 within sheath I3. When grid member I 8a is cast, itis cast around and shrunk upon heating element I0 so that heatingelement I0 is centrally located within the backbone portion 20 of gridmember I8a, as is best shown in Figures 4 and 5.

As pointed out hereinabove, the ns on grid member I 8a form passagewaysthrough which air centrally posiows as itis heated. The fins |9a and |9b(Figures 4 and 5) extend outwardly from each side of the backboneportion in pairs which are aligned with respect to each other. Thecenter portions of each pair of fins branch outwardly from sides o-fbackbone portion 20 of grid member ISa at uniformly spaced intervals ina direction taken from the front to the back of grid member |8a. The ns,with the exception of front fins 22 (Figure 3), are curved at theirbottom and top extremities to :facilitate the entrance of air into andexit of air from the passageways 2| and have a constant curvature at thebottom but a decreasing curvature relative to one another at the top sothat the cross sectional area of the upper portion of each passagewayconstantly increases as it is followed upwardly. This permits the air toexpand as it is heated while traveling upwardly thru the grid memberpassageway 2|. Fins 22 are fiat, extend outwardly from the sides ofthebackbone portion 2t adjacent ythel front edges thereof and theirAupper and lower endsare spaced from the upper and lowerv fins andpositioned' immediately rearwardly thereof.

Asis best shown in Figures 3 and 4, grid member IBa'is castr with abaseportion 23 'integral with backbone portion 20 and the lower ends of therear ns. Thus, a rugged, essentially one piece grid member has beendescribed which is highly efcient in converting electrical energy intoheat energy. The total radiating area of each of the grid members ismany times the sheath area of each heating element. Thus, each gridmember increases the convection surface of each heating element'to amaximum and this results in each grid member having a high B. t. u.outputat a low operating temperature for safety and long life. f

Aspointed out hereinabove, the grid members lcaglb, |86 and |8daremounted on connection box 24.7 The body 'of connection box 24 is castand includes four integral substantially vertical side walls arid-atop.VThe exterior surface of the top is datand-is machined to.0 02" feelergage to permit ai close nt"w'ith the bottom surface of eachf'of the gridmembers which are also machined vto the same tolerances. vided-with'napair of holes for each grid memb'er, Vsuchy as holes 43 and 44 (Figure3), thru lwhichmthe lower ends of the heating element of eachfgrid e,ber passinto the interior of the connection box when the grid membersare mounted thereon. The base of each grid member is secured tdI the topof the connection box by a pair'ofscrews such'as screws 25 (Figure 4).

The lower edges'of the four walls of connection box 24 are also machinedto close tolerances as well as the' top of a cover 21 so that cover 21fits the bottom of box 24 VveryV closely. Cover 21 isv secured to thewalls of 'the connection box by means of screws 28. Thus, all openingsthrough the top and bottom of the connection box are closed in such amanner that tight flame paths are provided, thus preventing any llamefrom reaching externally of connection box 24 should an explosion occurtherein. YConnection box 24 is of veryV heavy construction andisdesigned to withstand an'internal explosion pressure of 85 pounds persquare inch and a hydrostatic pressurefof 350 pounds per squareY inchplus an appropriate safety factor.

To permit electrical connections to be made to the terminals oftheheatingelements within the connection box, a'threafded hole is providedin The top is pro-y each of the end walls of connection box 24.Conduits, such as conduit 26, are threaded into these holes and hold thepower lines or wires which connect the terminals to the source of power.The input wires are housed within conduit 26 so as to insulate the wiresfrom any exposure to dangerous atmospheres, to reduce to a minimum thepossibility of access of dangerous atmospheres to the interior of theconnection box, and to' prevent any llame from any explosion occurringwithin the connection box from reaching externally thereof. The conduit26 also may be used to join two or more heaters in series if more thanone heater is to be used. If a heater is used alone, one of the holes inone of the ends of connection box 24 is plugged. Thus, the relativelysmall portion of the terminals and power lines which are in any wayexposed are protected from contact with any7 dangerous atmospheres inthe vicinity of the heater by being safely housed within box 24 andconduit 26 and should any explosion occur within the box, it will be.contained therein.

The assembly consisting of the grid members |8a, |812, |8c and |8d andconnection box 24 is mounted within housing 9 (Figure 2), which includesa rear plate 30, a baille 3| attached to plate 39, and a streamlinedfront cover 32 which is bolted to plate 30. Plate 30 essentiallycomprises a sheet of steel of rectangular shape, the upper4 and sideedges of which are flanged forwardly. To mount connection box 24 and thegrid members on housing 9, the rear surface of connection box 24 (Figure3) is provided with a pair of bosses, such as boss 49. A pair of screws,such as screws 29, pass through rear plate 30 and thread into each boxand rmly secure the grid members and connection box 24, plate 30, andthus housing 9.

Batlle 3| includes side walls 31a, and 3 lb and a rear plate 3 Ic, thelower portion of which is flat and which is curved at the top to conformsubstantially to the shape of the rear fins of the grid members. Batlle3| is attached by brackets 50 and 5| to rear plate 30 so that its rearsurface is spaced from plate 30, thereby permitting a secondarycirculation of air in this space, as indicated by the arrows 4B. The airpasses upwardly along the back plate between connection box bosses 49,and thus keeps rear plate 30 cool. A uniform separation is providedbetween plate 3 |'c and the rear grid member fins to permit upwardcirculation of air between the baiile andthe rearmost ns.

The housing cover 32 has a front, a top, and two sides, but is open atthe back'and bottom. It is fastened to the flanges on rear plate 30 bymeans of bolts, such as bolt 33 (Figure 3)'. Openings 9a'and 9b(Figure 1) :are provided. in the front portion of cover 32 correspondingin position to the entrances into and the exits from the passageways 2|between adjacent ns, s'othat air may circulate through the heater.Openingsv are also provided at the bottomof the sides to" permit theconnection of conduits, such as lcon'- duit 26. To permit the heatertobewcon'nected to a wall, mounting brackets 34 are attached 'tor therear surface of the rear plate 30.

In operation, electrical energy is converted inf to heat energy in theheating elements Il)J which` is transmitted through the gridl members tothe radiating surfaces of their ns. Cool air from the area to be heatedenters opening` 9d (Figure l), is heated as it flows upwardly throughthepassagewaysl 2| (Figure '3) and passes out ofn opening 9b (Figurel)`After leaving' the heater.'-

the warm air circulates through the room. At the same time, cool airflows upwardly between box 24 and baffle 3l and rear plate 3i). This airflows out of the housing between the upper edges of baille 3| (Figure 3)and opening 9b. This secondary air circulation keeps rear plate 30 cool.

There are many distinct advantages which the heater offers. Therelatively small radiating surface area of each heating element ismultiplied to a maximum when it is compared to the large radiatingsurface of the grid member it heats. This ensures maximum efficiency intransferring heat energy from the heating elements to the air beingheated. Because of the manner in which the grid members are constructed,any heat energy generated by the flow of current through the heatingelements is quickly conducted to the surface of the fins where it iscirculated by convection through the area to be heated. Even though acomplete heater weighing only about 85 pounds may draw as much as 2000watts, the maximum grid temperature will be less than 500 F., and themaximum temperature will be only about 150 F. on the wall to which theheater is fastened, the ambient temperature in the above tests being ashigh as 104 Also, it should be noted that the heating elements whichreceive electrical energy and convert it into heat energy are completelycovered throughout most of their length by grid members which serve totransmit the heat evenly to their entire radiating surface. In the smallareas Where the grid members do not cover the heating elements and whereelectrical connections are made to the heating elements, the electricalconnections and heating elements are completely enclosed in anexplosion-proof box which is so constructed that should an explosionoccur therein, it will be completely contained within the box. Theheater is composed of a minimum number of parts which may be assembledeasily and quickly and which provide a highly eliicient, safe,explosion-proof electric heater when once assembled. These advantages,in addition to the low operating temperatures of the grid memberscombined With their high B. t. u. output make it readily apparent thatthe heater has wide application Where safety is paramount, such as inpipe line pump houses, refinery meter houses, gasoline bulk stations,propane bulk stations and similar properties. It will thus be seen thata practical and eicient explosion-proof heater has been described inwhich the several objects hereinabove mentioned as well as many others,have been successfully accomplished.

Since many possible embodiments of the above invention may be provided,and since many changes may be made in the embodiment above set forth, itis understood that all matter hereinabove set forth or shown in theaccompanying drawing is to be interpreted as illustrative and not in alimiting sense.

I claim:

1. In a heater, in combination, a grid member including a backboneportion having a plurality ofl ns thereon, said backbone portionincluding a base portion, an electric heating element cast within thebackbone portion of said grid member and having its terminals extendingfrom said base portion, a connection box including four walls and anintegral top, said terminals extending through said top into theinterior of said connection box, means connecting said base portiontightly to the top of said connection box, and a cover closing thebottom of said connection box.

means connecting said cover tightly to said box, the engaging surfacesof all portions of said connection box, said base portion and said coverbeing smooth to t closely to thereby provide tight ame paths from theinterior of said connection box to the exterior thereof whereby theflame resulting from any explosion in the interior of said connectionbox will be completely dissipated in said flame paths before reachingthe exterior ofv said connection box.

2. In a heater, in combination, a housing, said housing including afront Wall, two side walls, a rear plate and a top, a plurality of gridmembers, each of said grid members including a, backbone portion and aplurality of fins extending outwardly therefrom, the front portion ofsaid housing including spaced openings positioned one above the other,said fins and said grid members being shaped to form passagewaysconnecting said upper and lower openings in said front wall, a heatingelement cast within the backbone portions of each of said grid members,a connection box, the terminals on said heating elements extending intosaid connection box, said connection box completely enclosing saidterminals and al1 electrical connections thereto, all exits from theinterior of said connection box to the exterior thereof being tightlyclosed, said connection box being connected to but spaced from said rearplate, and a baille spaced from but conforming to the shape of the rearsurfaces of the rearmost ns of said grid members, the upper end of saidbaille being positioned beneath the lower edge of the upper opening insaid housing, said baille also being spaced from said rear plate wherebyair ows upwardly between said fins and baille and said baffle and rearplate and thence flows out of said housing through the uppermost openingtherein, said air absorbing the heat radiated by the rearmost ns andthus preventing excessive heating of said rear plate.

3. In an electric space heater, in combination, a grid elementcomprising a vertical elongated backbone member, an electric heatingelement associated with said backbone member, and a plurality of finsprojecting horizontally from each side of said backbone member, saidfins having vertical middle portions and ends curving toward the frontof said backbone member thereby forming passageway to guide air beingheated from the bottom of said grid element to the top, the top ends ofsaid ns being spaced further apart than the bottom ends thereof toincrease the size of said passageways at the top and thereby increasethe free flow of air as it is expanded on heating.

4. In an electric space heater, in combination, a grid elementcomprising a backbone member having a plurality of i'lns for heating andguiding air and a flat base portion integral With said backbone member,an electric heating element in said backbone member and having itsterminals extending from said base portion, a connection box connectedto said base portion of said grid element, said terminals extendingthrough holes in the adjacent side of said connection box, the engagingsurfaces of said element and box being machined flat, and a conduit ttedto said connection box for shielding a power line to said terminals,said connection box having a machined lower peripheral edge and a bottomcover which ts to said edge, the bottom cover and base portions beingmachined to t said connection box and provide tight flame paths from theinterior of said connection box to the exterior thereof.

5. In an electric space heater, in combination,

agotarse 7 a; heating eiefet *ha-ving, a `maeiii'ned lbase portion -withterminals extending therefrom, 'a -con-v nection box 'having a machinedtop for'receiving saidba'se portion, holes for said terminals and 'amachined lower peripheral edge, a'bottom cover machined to't said edge,and means fior "connecting said base :portion and said-cover firmly tosaid connection '150x 'to provide tight name paths from the interior ofsaid connection box,

said connection box and said coverbeing 'heavilyv surfaces, and meansfor fastening said cover tol :said box to form a tight it therewith, theedges of -said box being suic'iently thick so that. said :surfacesbetween said 'cover vand said boxform a .ame path suiiicient todissipate all heat to a non-combustible temperature Vbefore it escapesto theatmosphere.

7, In a space heater, in combination, a "grid member comprising avertical backbone element, heating' means associa-ted with said backboneelement, and a plurality of iins projecting horizontally from saidbackbone element thereby forming passageways to guide air being heatedfrom the bottom of said lgrid memberV to the top, said iin's comprisingverticall portions curved at their bottom and top extremities tofacilitate entrance of air into and exit'of air from said passagewaysAand having a constant curvature at the bottom but a decreasingcurvature relative to one another at the` topiso thatV the crosssectional area of the upperA portion of each passageway constantlyincreases as4 it is followed upwardly, thereby permitting air to expandas it is heated while ris,- ing through said passageways. l

3,' In a space heater, in combination,A a heatingelement and a housingenclosing said heating element, said housing having a vertical Wall witha'pair of spaced openings positioned one above the other, and saidheating element comprising a vertical backbone member, heatingmeansassociated with said backbone member, and a plurality of nsprojecting horizontally from said back; bone member, said ns beingspaced from each other and having vertical portions curved at theirvertical spaced respective'extremities toward said housing openings, toform passageways for guiding air being heated from the bottom opening upthrough said housing and out the top opening.

'9. In a's'pac'e heater, in-combination, a heating element anda housingenclosing said heating-lele; ment, said housing having a verticalwallwith a pair of spaced openings positioned one "above the other, and saidheating element comprising a backbone portion, a plurality of nsextending o'utw'arcllyy thereof, and heating means associated with: saidbackbone portion, said iin's being'shaped to'fform passageways toconnect said openings and to increase the cross sectional area of theupper portion of each of said passageways, thereby-directi'ng airadmitted inthe lower of said openings through said passageways and outtheV uppercf said openings and thereby permitting said air to expandfre'elyj as it is heated.

1G. An explosion proof terminal connection box comprising, incombination, a box member fone side of which is open, a conduit fittedto said box member for shielding a power line leading tothe interior ofsaid box, said box member having openings in one of its-walls forreceiving electrical terminals and having a machined flat surfaceadjacent said terminal openings, the marginal surface adjacent the openside of said box being .machined flat, electrical apparatus withterminals extending through said openings and having a machined surfacewhich is tightly secured to said wall of said box to cover said terminalopenings and to provide tight flame paths leading therefrom between saidbox and said electrical apparatus, a cover for said box machined to ttight upon the marginal surface adjacent the open Aside of the box, andmeans to secure` said coverv tightly to said box to provide tight namepaths leading from the interior` thereof whereby tight flame paths areprovided from all points in the interior of said box member to dissipatecompletely all flame resultingV from an explosion Ain the interior ofsaid box to a noncombustible temperature before it reaches theatmosphere. f

LOWELL R. MAST.

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